Dispersant used to clean oil spill more harmful to corals than the oil

The largest accidental marine oil spill in the history of the petroleum industry is the Deepwater Horizon oil spill in 2010. The corrective measure taken was using dispersants to dissipate the oil, but it’s been found that this chemical dispersant is more toxic to cold-water corals than the oil itself, according to a study conducted at Temple University.

This research finding titled “Response of deep-water corals to oil and chemical dispersant exposure,” was published online in the journal Deep-Sea Research II.

Approximately five million barrels of crude oil escaped from the well drilled by the Deepwater Horizon oil rig in 2010, and nearly seven million litres of dispersants, chemical emulsifiers were used to break down the oil and to clean it up.

Dispersants were used as a first line of defence even though little was known about how they affect microbial communities. Normally these dispersants are applied to the water’s surface, but the spill marked the first time that dispersants were applied at depth during an oil spill. The main idea was to immediately do something about the oil coming out of the well, but they really didn’t know what was going to happen as a result.

Following the 2010 spill, Cordes and his collaborators discovered several Gulf (Gulf of Mexico) corals were damaged; they were coated with a dark-colored flocculent slime that was found to contain oil from the spill and residues from the dispersants. They wanted to know if the damages could have been caused by the oil, the dispersant itself, or a combination of both.

A coral specimen exposed to oil and dispersant displays declining health over time. Credit: Courtesy of Erik Cordes/Temple University

“We know that the corals in the Gulf were exposed to all of these different combinations, so we have been trying to determine the toxicity of the oil and the dispersants, and see what their impact would be on the corals.” said Danielle DeLeo, a Temple doctoral student in Cordes’ lab, who was the study’s lead author.

The researchers exposed 3 cold-water coral species from the Gulf to various concentrations of the dispersant and oil from the Deepwater Horizon well to determine a lethal dose for each. They were surprised to find that the lethal concentration is much lower for the dispersant which means the dispersant is toxic to the corals at lower concentrations than the oil. And, combination with the dispersant increases the toxicity of oil, Cordes added.

Cordes said that his lab will be carrying out additional studies to try to replicate the concentrations of oil and dispersant that the corals were exposed to during the Gulf oil spill, but this is the first step in determining the toxic levels of dispersants and their impact on the environment.

Their findings could assist in developing future strategies for applying dispersants at oil spills that may be more helpful than harmful to the environment.